WASHINGTON, April 2 (Reuters) - The U.S. military has spent more than $3.3 million on the search for missing Malaysia Airlines Flight MH370 and has put in place plans that nearly double the original $4 million available for the hunt, a Pentagon spokesman said on Wednesday.

Army Colonel Steve Warren said the Defense Department spent $3.2 million between March 8 and March 24 on the initial search for the Boeing 777-200ER, which went missing more than three weeks ago during a flight from Kuala Lumpur to Beijing.

Those funds came from $4 million that Defense Secretary Chuck Hagel initially authorized in spending from the Pentagon's Overseas Humanitarian Disaster and Civic Aid fund, he said.

As the search for the missing plane shifted to the southern Indian Ocean, the Pentagon's contribution to the effort narrowed to flying Navy P-8 surveillance planes out of Perth, Australia.

Funding for the effort then shifted to the Navy's Operations and Maintenance budget. Between March 25 and March 31, the Navy spent about $148,300 to fly its P-8s in the ocean search mission, he said.

The Pentagon also responded to a Malaysian request to provide underwater search equipment, sending a Towed Pinger Locator as well as a Bluefin-21 autonomous underwater vehicle. Both devices can be used to listen for pinging sounds emitted by the plane's flight data recorders.

Warren said no specific limit had been set on the funding for flying the P-8s. He said the Pentagon had set an initial budget of $3.6 million for the underwater search equipment being provided by the Naval Sea Systems Command. That gear is still en route to the search area.

"That's how much we've budgeted for the pinger and the Bluefin," Warren said. "We don't have an exact cost yet because it's going to vary depending on how much it gets used."

Up to 10 planes and nine ships from a half dozen countries on Wednesday scoured a stretch of ocean roughly the size of Britain, where the Malaysia Airlines jetliner is believed to have crashed.

Authorities have not ruled out mechanical problems as causing the disappearance, but say all the evidence suggests the plane was deliberately diverted from its scheduled route. (Reporting by David Alexander; Editing by Paul Simao)